1. Field of the Invention
The present invention is related to a miniature brushless dc fan motor and more particularly to a permanent magnet set incorporated into a center of a fan wheel, and plural coils incorporated into an annular housing, thereby forming an air channel between the permanent magnet set and the coils.
2. Description of the Related Art
Referring to FIG. 1, a conventional miniature fan 1 includes a bearing assembly 11, a stator 12 and a rotor 13. The bearing assembly 11 includes at least one bearing located at a center of the stator 12. The stator 12 is provided with a plurality of coils 121 and a plurality of pole plates 122. After assembling, the bearing assembly 11 and the stator 12 are co-axially fixed at a center of a fan housing 10. The rotor 13 includes a shaft 131, a permanent magnet set 132 and a blade set 133. The shaft 131 of the rotor 13 extends through the bearing assembly 11 to nest the stator 12 in the rotor 13 and thus the miniature fan 1 is assembled. So then the blade set 133 is extended outward from the outer circumference of the rotor 13 and adapted to drive air.
The assembled arrangement of the blade set 133, the permanent magnet set 132, the coils 121 and the bearing assembly 11 is nested in order from a maximum diameter to a minimum diameter. In addition to the blade set 133, a radial air gap must further be provided between the permanent magnet set 132 and the coils 121 to thereby induce mutually and rotate the rotor 13. Consequently, the diameter of the miniature fan cannot further be reduced and thus such structural arrangement is unsuitable for miniature fan manufactures.
Referring to FIG. 2, an another conventional miniature fan 2 includes a bearing assembly 21, a rotor 22 and a stator 23. The bearing assembly 21 includes at least one bearing located at a center of stator 22. The rotor 22 includes a permanent magnet set 221 and a blade set 222 whose outer circumference is surrounded by the permanent magnet set 221. After assembling, the bearing assembly 21 and the rotor 22 are co-axially mounted to a center of a fan housing 20. The stator 23 includes a coil set 231 and a plurality of pole plates 232, which are secured to an inner circumference of the fan housing 20. So then the blade set 222 is extended between the axial assembly 21 and the stator 23 and adapted to drive air.
The assembled arrangement of the coil set 231, the permanent magnet set 221, the blade set 222 and the bearing assembly 21 is nested in order from a maximum diameter to minimum diameter. In addition to the blade set 222, a radial air gap must further be provided between the permanent magnet set 221 secured to the outer circumference of the blade set 222, and the coil set 231, thereby the coil set 231 able to induce with the permanent magnet set 221 and rotate the rotor 22. Consequently, the diameter of the miniature fan cannot further be reduced and thus such structural arrangement is unsuitable for miniature fan manufactures.
The present invention intends to provide a miniature brushless dc fan motor, wherein a permanent magnet set incorporated into a center of a fan wheel and, plural coils incorporated into an annular housing, thereby increasing a sectional area of an air channel formed between the permanent magnet set and the coils in such a way to mitigate and overcome the above problem.
The primary objective of this invention is to provide a miniature brushless dc fan motor, which includes a permanent magnet set incorporated into a center of a fan wheel and, plural coils incorporated into an annular housing, and an air channel formed between the permanent magnet set and the coils so that a sectional area of the air channel is increased.
The miniature brushless dc fan motor in accordance with the present invention comprises an annular housing, a bearing assembly, a permanent magnet set, a blade set and a coil set. The permanent magnet set is inserted into a hub of the blade set which is located at a center. A shaft is extended through the permanent magnet set to form a rotor. The coil set is secured to an inner circumference of the annular housing and radially aligned with the permanent magnet set. An air channel is formed between the permanent magnet set and the coil set, and adapted to accommodate the blade set.